Coal-based integrated gasification combined cycle plant (IGCC) technology enables production of electricity with a gas turbine utilizing a fuel that is rich in hydrogen and has a very limited amount of CO2. Combustion of the hydrogen-containing fuel requires an oxidizing source such as air, which contains nitrogen (N2). As a result, a by-product in exhaust gas stemming from hydrogen-containing fuel combustion is a significant amount of NOx. The NOx in the exhaust gas may be reduced by using selective catalytic reduction (SCR) systems along with low NOx combustors in the gas turbine. Since fuel produced and used at an IGCC plant contains hydrogen (H2), the fuel may also provide hydrogen as a reducing agent in the SCR process by introducing a small amount of H2 from the fuel supply into the SCR system. The use of hydrogen as a NOx reducing agent enables the elimination of typical reducing agents, for example, ammonia (NH3) and urea (N2H6CO) in the SCR system, and thus prevents discharge of ammonia slip into the ambient air, which is an inherent problem with current ammonia-based SCR technology.
Recently, a strong attempt to improve H2-SCR efficiency with respect to NOx removal and N2 selectivity under oxidizing conditions was made in U.S. patent application Ser. No. 12/122,116, the entirety of which is hereby incorporated by reference. As described in U.S. patent application Ser. No. 12/122,116, a palladium (Pd) catalyst showed a substantial increase in NOx reduction efficiency over a platinum (Pt) catalyst that was disclosed in U.S. Pat. No. 7,105,137, for example, under gas turbine exhaust conditions. In U.S. patent application Ser. No. 12/472,633, the entirety of which is also incorporated by reference herein, the Pd-based catalyst system was further modified by incorporating a pre-sulfated zirconium binder. While not wishing to be bound by any particular theory, the inventors believed that the pre-sulfated zirconia binder protects the palladium catalyst from degradation by binding sulfur to the defects in the crystalline zirconia structure, thereby minimizing further sulfur poisoning during contact with an exhaust gas containing SO2.